Synthesis, crystallographic characterization and ionic conductivity of iron substituted sodium zirconium phosphate Na1.2Zr1.8Fe0.2(PO4)3

Abstract

Sodium zirconium phosphate NaZr2P3O12 (hereafter NZP) crystallizes in rhombohedral (hexagonal) symmetry with the space group R-3c. The NZP-related phase of synthetic iron substituted NZP has been prepared by partial substitution on zirconium site by Fe(III). The material has been synthesized by sintering the finely powdered oxide mixture in a muffle furnace at 1,050 °C. The polycrystalline phase of Na1.2Zr1.8Fe0.2(PO4)3 has been characterized by its typical powder diffraction pattern. The powder diffraction data of 3,000 points have been subjected to general structural analysis system (GSAS) software to arrive at a satisfactory structural fit with R p = 0.0623 and R wp = 0.0915. The following unit cell parameters have been calculated: a = b = 8.83498(18) A, c = 22.7821(8) A and α = β = 90.0° γ = 120.0°. The structure of NZP consists of ZrO6 octahedra and PO4 tetrahedra linked by the corners to form a three-dimensional network. Each phosphate group is on a two-fold rotation axis and is linked to four ZrO6 octahedra. Each zirconium octahedron lies on a threefold rotation axis and is connected to six PO4 tetrahedra. AC conductivity of the solid solution has been measured between 303 and 773 K. The material exhibits temperature-dependent enhancement of ionic conduction by ≈400 times at elevated temperatures. The activation energies show significant change in slope at 1,000/T = 2.23(448 K).